Ayuso-Parrilla M S, Martín-Requero A, Pérez-Días J, Parrilla R
J Biol Chem. 1976 Dec 25;251(24):7785-90.
The effect of glucagon on hepatic protein systhesis and proteolysis has been investigated. The intraperitoneal administration of 200 mug of glucagon produced an increase of the polypeptide chains completion time which was maximal 5 min after its administration and approached control values at 20 min. The increase of the polypeptides chains completion time observed at 5 min after the hormone administration represents a 38% inhibition of the hepatic protein synthetic rate. When glucagon was continuously supplied by intravascular infusion, maximal inhibition was attained throughout the experiment. This inhibition of protein synthesis brought about by glucagon was accompanied by an increase in the polyribosomal state of aggregation, indicating that the hormone acts mainly if not exclusively, on the elongation or termination step, or both. The administration of glucagon produced also a progressive increase in the hepatic valine concentration. This increase could not be accounted for the the decrease in plasma valine levels, suggesting that the rise in haptic valine concentration is an expression of hepatic proteolysis rather than the result of an accelerated transport of amino acids across the hepatocyte plasma membrane. The different time sequence in the glucagon-induced effects of protein synthesis and proteolysis suggests that both effects are independent and probably mediated by different mechanisms.
已经研究了胰高血糖素对肝脏蛋白质合成和蛋白水解的作用。腹腔注射200微克胰高血糖素会使多肽链完成时间增加，给药后5分钟达到最大值，20分钟时接近对照值。激素给药后5分钟观察到的多肽链完成时间增加代表肝脏蛋白质合成速率受到38%的抑制。当通过血管内输注持续供应胰高血糖素时，在整个实验过程中达到最大抑制。胰高血糖素引起的这种蛋白质合成抑制伴随着多核糖体聚集状态的增加，表明该激素主要（如果不是唯一的话）作用于延伸或终止步骤，或两者兼有。胰高血糖素的给药还使肝脏缬氨酸浓度逐渐增加。这种增加不能用血浆缬氨酸水平的降低来解释，这表明肝脏缬氨酸浓度的升高是肝脏蛋白水解的表现，而不是氨基酸跨肝细胞膜加速转运的结果。胰高血糖素诱导的蛋白质合成和蛋白水解作用的不同时间顺序表明这两种作用是独立的，可能由不同的机制介导。
